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A Level Computer Science > 1.2.1 Operating systems > Flashcards

1.2.1 Operating systems Flashcards

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1
Q

Operating systems

Define ‘kernel’

A

The kernel loads and unloads software into main memory

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2
Q

Operating systems

Define ‘driver’

A

Controls and communicates with hardwaere

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3
Q

Operating systems

Define ‘utilities’

A

Programs that perform background tasks

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4
Q

Operating systems

Define ‘user interface’

A

A way to allow users to interact with the computer system

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5
Q

Operating systems

Define ‘operating system’

A

Software which controls how a computer operates

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6
Q

Operating systems

Define ‘scheduling’

A

The process of assigning resources to tasks

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7
Q

Memory management

Describe the process of memory management

A

Ensuring programs cannot access each other’s data

Ensuring the RAM’s free space is being used efficiently

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8
Q

Memory management

What are the two methods of managing the space used in main memory?

A

Paging

Segmentation

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9
Q

Memory management

What is memory segmentation?

A

The allocation of segments of memory to a process, to allow it to run

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10
Q

Memory management

What sections are found within each segment during memory segmentation?

A

Stack segment

Free memory

Data segment

Code segment

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11
Q

Memory management

What is the role of the code segment?

A

Where the program instructions for the process reside

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12
Q

Memory management

What is the role of the data segment?

A

Memory space for the variables the program will use

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13
Q

Memory management

What is the role of the stack segment?

A

Stores the address of the line in the program the processor was on when it got interrupted by a subroutine

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14
Q

Memory management

What is the role of the free memory?

A

Available memory space put aside for the stack overflow

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15
Q

Memory management

What is virtual memory?

A

An area on the hard disk that has been marked as additional main memory, to increase the size of RAM temporarily

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16
Q

Memory management

How does the CPU access data held in virtual memory?

A

The memory manager swaps data between RAM and virtual memory for the CPU to access, as it can only reach data stored in RAM

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17
Q

Memory management

What is meant by ‘disk thrashing’?

A

When the hard disk is excessively used for virtual memory storage, and data is being transferred repeatedly between RAM and virtual memory

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18
Q

Memory management

What is a ‘page’?

A

A fixed sized area of memory

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19
Q

Memory management

How does the memory manager keep track of pages?

A

Each page has an associated number, kept track of in a page table

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20
Q

Memory management

What happens when RAM is getting full, in regards to memory being stored as pages?

A

The memory manager identifies less used pages and cuts them to virtual memory

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21
Q

Memory management

Describe what pagination is and when it is used

A

Pagination is the process of separating memory into pages

It is used when managing and using virtual memory

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22
Q

Memory management

What are the similarities between segmentation and pagination?

A

Both are a way of dividing up memory

Both are assigned and managed by the memory manager

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23
Q

Memory management

What are the differences between segmentation and pagination?

A

Segmentation is used to load and unload processes, whereas paging is used when swapping data to virtual memory

The size of a segment always varies, whereas a page is a fixed size

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24
Q

Memory management

What is a ‘memory leak’, and what can happen because of one?

A

A memory leak is when segments contained finished with processes aren’t remarked as free, and therefore prevent more data from being stored in memory

Due to a memory lea, the system can eventually run out of memory

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25
Q

Memory management

What is a ‘stack overflow’?

A

When the stack section in a segment has run out of free memory to expand into, causing the program to crash with a stack overflow error

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26
Q

Interrupts and scheduling

What is meant by ‘polling’?

A

The regular checking of devices or software to ensure it doesn’t have problems

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27
Q

Interrupts and scheduling

What is an advantage and disadvantage of polling?

A

Advantage:

Simple and predictable as it only occurs at specific points

Disadvantage:

Can be inefficient as it uses up CPU processing time

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28
Q

Interrupts and scheduling

What is meant by the term ‘interrupt’?

A

A signal for the CPU to stop what it is doing and carry out the interrupt task

Afterwards it will go back to what it was originally doing

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29
Q

Interrupts and scheduling

Explain the process for the CPU upon receiving an interrupt

A
  • An interrupt arrives while the CPU is running its current program
  • It comes with a priority label telling how important it is
  • If it is more important than the current process, the CPU will jump to the task the interrupt is asking the CPU to carry out, an ISR (Interrupt Service Routine)
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30
Q

Interrupts and scheduling

What happens to the values in the registers when a higher priority interrupt comes in

A

All the values in the registers are copied to the stack segment whilst the CPU executes the ISR

After it is completed the stored values are loaded back into the registers

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31
Q

Interrupts and scheduling

What is context switching?

A

The moving of instructions from the current CPU operation to the ISR and back

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32
Q

Interrupts and scheduling

What are two problems caused by using interrupts?

A

Latency

Stack overflow

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33
Q

Interrupts and scheduling

Describe latency, in regards to interrupts

A

Latency is the delay between an input into the system and the desired output

This can be extended if the CPU keeps receiving interrupts

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34
Q

Interrupts and scheduling

Explain what an ISR is

A

Interrupt Service Routine

A software routine that hardware invokes in response to an interrupt

ISRs examine an interrupt and determine how to handle it

35
Q

Interrupts and scheduling

What are 3 examples of interrupts, in priority order highest to lowest

A

Power fail interrupt

Clock interrupt

An I/O device sending a signal requesting service, or signaling the end of an I/O operation

36
Q

Interrupts and scheduling

What is meant by the term ‘scheduling’?

A

The allocation of CPU processor time to all running programs

37
Q

Interrupts and scheduling

What are 5 scheduler methods?

A

First Come, First Served

Round Robin

Shortest Job First

Shortest Time Remaining

Multi-Level Feedback Queue

38
Q

Interrupts and scheduling

How does FCFS work?

A

First Come, First Served

All processes are put in a queue

Each is allowed to run to completion, before then loading the next one in the order they arrived

39
Q

Interrupts and scheduling

What are the benefits to FCFS?

A

Simple to implement

Ensures that once a process starts it runs to completion in minimal time

40
Q

Interrupts and scheduling

What are the drawbacks to FCFS?

A

Once one starts it prevents other jobs from being processed

Doesn’t account for priority

Doesn’t consider process lengths

41
Q

Interrupts and scheduling

How does RR work?

A

Round Robin

All processes are held in a queue

Each one is given a set amount of time

If not completed the next one is loaded and the process joins the back of the queue

42
Q

Interrups and scheduling

What are the benefits of RR?

A

Simple to implement

Good if all processes are a similar priority and size

43
Q

Interrupts and scheduling

What are the drawbacks of RR?

A

Doesn’t account for the priority of a process

Doesn’t consider the process length

If the processes are different in priority and length it becomes inefficient

44
Q

Interrupts and scheduling

How does SJF work?

A

Shortest Job First

Arranges processes in a queue with the shortest first

Length is considered in number of fetch-execute cycles required

45
Q

Interrupts and scheduling

What are the benefits of SJF?

A

Ensures maximum number of jobs are completed

Ensures short jobs aren’t kept waiting

Minimises average time a process takes to complete

46
Q

Interrupts and scheduling

What are the drawbacks of SJF?

A

Doesn’t account for priority

A long job will still be interrupted for a shorter job

Longer jobs might never complete if shorter jobs keep joining the queue

47
Q

Interrupts and scheduling

How does STR work?

A

Shortest Time Remaining

Arranges processes in a queue with those with the least cycles remaining first

48
Q

Interrupts and scheduling

What are the benefits of STR?

A

Allows shorter processes to be handled quickly

Ensures the maximum number of processes are completed in a given time, accounting for what has already happened

49
Q

Interrupts and scheduling

What are the drawbacks of STR?

A

Doesn’t account for priority

Particularly long jobs might never be completed if shorter jobs keep joining the queue

50
Q

Interrupts and scheduling

How does MLFQ work?

A

Multi-Level Feedback Queue

Contains multiple queues, each with a different priority level

Each individual queue is sorted by the of the other scheduling methods

The higher priority queue is completed first

51
Q

Interrupts and scheduling

What are the benefits of MLFQ?

A

Makes use of priority

Ensures the higher priority processes run on time

52
Q

Interrupts and scheduling

What are the drawbacks of MLFQ?

A

Complex to implement

Not efficient if all jobs have a similar priority

Low priority jobs may take a really long time to complete

53
Q

Types of operating systems

What are 5 types of operating systems?

A

Distributed

Embedded

Multi-tasking

Multi-user

Real time

54
Q

Types of operating systems

What is a distributed operating system?

A

The OS controls a number of computers, called a cluster, in order to undertake a single computer-intensive task

55
Q

Types of operating systems

How does a distributed operating system work?

A

The OS controls many computers at the same time

Each node contains part of the overall operating system

The user is aware of only using one powerful machine

56
Q

Types of operating systems

What are some examples of where a distributed operating system is used?

A

To render animations

Work on scientific / mathematics problems

57
Q

Types of operating systems

What is an embedded operating system?

A

An OS contained in a computer which can be found within many types of electrical equipment, to control its operations

58
Q

Types of operating systems

How does an embedded operating system work?

A

The hardware is designed to handle a specific task on a specific system, often performing actions in real time

59
Q

Types of operating systems

What are some examples of where an embedded operating system would be used?

A

Cars

To control equipment

ATMs

60
Q

Types of operating systems

How does a multi-tasking operating system work?

A

The OS appears to be multiple processors running at once

61
Q

Types of operating systems

How does a multi-tasking operating system work?

A

The schedular manages the swapping of processes in and out of the CPU so they all run as close to simultaneously as possible

They all appear to be running at the same time to the user, allowing multiple programs to run at the same time

62
Q

Types of operating systems

What is an example of where a multi-tasking operating system would be used?

A

On most personal computers

63
Q

Types of operating systems

How does a multi-user operating system work?

A

It allows multiple users on different workstations to all access the same central computer, which contains the OS

64
Q

Types of operating systems

How does a multi-user operating system work?

A

The OS divides up CPU processor time between each workstation

It therefore performs similarly to a multi-tasking OS, just with different users rather than different processes

65
Q

Types of operating systems

What is an example of where a multi-user operating system would be used?

A

In automated checkouts connected to an office mainframe

66
Q

Types of operating systems

How does a real time operating system work?

A

The OS is designed to handle input data within a specific time interval

67
Q

Types of operating systems

How does a real time operating system work?

A

It is designed to be extremely reliable, precise and consistent

Handles inputted data in priority order, and outputs results within a guaranteed time

68
Q

Types of operating systems

What are some example of where real time operating systems are used?

A

Factory production lines

Washing machines

Hospitals

69
Q

Types of operating systems

What are the key features of a distributed operating system?

A

Contains many computers

Can process very intensive tasks

Example of parallel processing

70
Q

Types of operating systems

What are the key features of an embedded operating system?

A

Is inside an electrical device

Performs a specific set of processes

Generally doesn’t multi-task

71
Q

Types of operating systems

What are the key features of a multi-tasking system?

A

Appears to run concurrently

Continuously swapping tasks in and out of the CPU

72
Q

Types of operating systems

What are the key features of a multi-user system?

A

One central mainframe with the OS installed

Many workstations connected to the central node, sharing the OS

73
Q

Types of operating systems

What are the key features of a real time operating system?

A

Designed to handle things in determined time intervals

Used for functions requiring precision and consistency

74
Q

Virtual machines

What is a virtual machine?

A

A software copy of a type of computer

It is created inside another computer

75
Q

Virtual machines

What are the benefits of using a virtual machine to a non-programmer

A

Can run older applications no compatible with the current computer model

Can run multiple operating systems on the same computer

Easy to copy and backup

Can be used to inspect possible malware/viruses so the main computer isn’t affected

76
Q

Virtual machines

What are the disadvantages of virtual machines to non-programmers?

A

Programs run less efficiently on a VM than on the original hardware

A proper license is still needed to run the OS and associated applications on the VM

The VM can’t use more resources than your computer actually has

77
Q

Virtual machines

What is an advantage of virtual machines to programmers?

A

Programs and code are portable, as they can be run on any hardware that has the same type of VM, with always the same source code

78
Q

Virtual machines

What is a disadvantage of virtual machines to programmers?

A

Some VMs can have different levels of security, compatibility or run speeds

Additionally, not all will have the latest protection software

79
Q

BIOS

What is BIOS?

A

Basic Input / Output System

It is a system as part of the operating system, which handles the input and outputs of the computer

It is stored on the ROM chip and runs as part of the start-up sequence

80
Q

BIOS

What is EEPROM?

A

Electrically Erasable and Programmable Read Only Memory

It is another name for the ROM chip

81
Q

BIOS

What are the start-up sequence steps, up to the POST?

A
  • Power supply fires up
  • The first instruction on the BIOS chip is loaded along the control bus
    • The RAM will be empty at this point
82
Q

BIOS

What is the POST, performed during the start-up sequence?

A

Power On Self-Test, when BIOS checks:

  • BIOS isn’t corrupted
  • System chips are ok
  • Processor is ok
  • Memory is ok
  • Keyboard is present
  • Video display hardware present and ok
83
Q

BIOS

What are the start-up sequence steps after POST?

A
  • If any problems arose during the POST checks beeps are emitted to signal them
  • Internal hardware is booted up, with instructions the hardware requires also getting run
  • The MBR (Master Boot Recorder) is found on the hard disk, and tells the CPU where the OS is stored, and how memory is partitioned
  • Then BIOS will search for the OS through the storage devices connected by the boot order (list of places to check)
  • Finally, a boot file is run with all the user’s personal setup information

A Level Computer Science (20 decks)

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